Simulating X-ray Spectra with Q-Chem

  • In Q-Chem, the truncated excitation space and core-valence separation approximations are adopted in the time-dependent density functional theory (TDDFT), equation-of-motion coupled cluster (EOM-CC) and algebraic diagrammatic construction (ADC) frameworks, which enables calculations of core-excited and core-ionized states and relevant spectroscopic properties.

  • EOM-CC and ADC are high-level correlated methods which can offer accurate simulated X-ray spectra.

  • TDDFT has a good balance between computational accuracy and cost, making it a widely used tool in X-ray spectroscopy simulation.

  • XAS (X-ray absorption), XPS (X-ray photoelectron), XES (X-ray emission) and RIXS (resonant inelastic X-ray scattering) spectra can be simulated.

  • Transition properties between valence and core-level states can be calculated.

  • The simulated spectral features can be analyzed with natural transition orbitals and Dyson orbitals, both of which can be visualized with IQmol.

  • Solvent effects can be included explicitly via QM/MM and effective fragment potential (EFP).

Simulated XAS of butadiene using TDDFT

Simulated C K-edge RIXS of benzene using EOM-CC Simulated C K-edge XPS of adenine using EOM-CC

Simulated O K-edge XES of H2O using ADC